I've been using HyperDrive SPACE for half a year now, and have very positive experiences. It's a portable HDD with a built-in card reader and seems to fulfill your requirements. It's a bit bigger than a deck of cards. It has longer battery life than every competitor I know of. And it's faaaast, so fast that I've used it as an external HDD for everyday computer use. It doesn't have a viewing screen, which I don't need - the screen on the SPACE is for the UI only. If you do need a proper viewing screen, there are offerings from other companies (Lacie and Epson, I believe) which have a screen but a much bigger price tag.
If you get the SPACE, I recommend buying the housing only, and getting the 2.5" portable HDD from a discount vendor, and installing the HDD yourself. It's very easy with the instructions and tools provided with SPACE, and saves you quite a bit of money.